For instance this A2 handguard is exactly 12". In the same manor measured, how long are the mid-length guards?

I am going to build a mid-length barrel out of a standard M4 barrel, but I have to know if the mid-length handguards are long enough to extend over the (original) milled off front sight. The new front sight base is going to be a weaver gas block w/detachable sight.